1. Field of the Invention
This invention relates generally to exhaust systems. More particularly, the invention relates to an exhaust system for a multi-cylinder internal combustion engine.
2. Background
Motorcycles commonly employ exhaust systems to convey the exhaust gas from the engine's cylinder to the ambient environment. The journey begins at the engine cylinder, which incorporates intake and exhaust ports for ingress and egress to the cylinder. Fresh air mixed with fuel enters the engine cylinder through the intake port where it is subsequently compressed by a piston and ignited. A rapid expansion of the compressed fuel and air occurs, thereby forcefully moving the piston in the opposite direction to the compression stroke. Once the expansion is complete, the exhaust port opens to allow the combustion by-products or gas to exit the engine cylinder and enter an exhaust pipe. The exhaust port may be a passageway into the engine cylinder that is uncovered by the retreating piston, as in a two-stroke design well known in the art. In the case of a four-stroke design, a valve is utilized to open or close the exhaust port. The exhaust gas expelled from the engine cylinder, after passing through the exhaust port, enters an exhaust pipe. The exhaust pipe is designed to direct the exhaust gas towards the rear of the motorcycle and commonly utilizes bends and curves to accomplish this goal.
In the case of a V-Twin Harley-Davidson® motorcycle engine, the design of the stock OEM exhaust system affects the motorcycle's performance. The OEM exhaust system comprises a partial dual exhaust system with unequal length exhaust pipes from each cylinder. This system allows some communication between the exhaust gases from the cylinders via a crossover pipe. However, the design of this crossover pipe is detrimental to the engine's performance. The exhaust gases from the cylinders interfere with each other as they are routed to two exhaust mufflers. Moreover, the routing path of the gases from the engine exhaust ports to the exhaust mufflers increases the exhaust systems backpressure.
The design of the stock OEM exhaust system for the V-Twin Harley-Davidson® motorcycle also affects the aural sensation experienced by the rider. For example, the sound of the OEM exhaust system is uneven as heard by the rider due to the exhaust system's design. Further, during the engine's transition from under load to a state of deceleration, the engine emits a staccato popping sound that is not pleasing to the ear. Any potential aftermarket fix for these performance and aural sensation issues is further complicated by the design of the Harley-Davidson® OEM exhaust system which attaches to the chassis of the motorcycle at fixed points, thus impeding any modifications to the exhaust system without permanent changes to the motorcycle.